Sensors for measuring redox reactions are known in the art. U.S. Pat. No. 4,545,382 to I. J. Higgins et al discloses a glucose sensor wherein glucose oxidase is immobilized at the surface of a ferrocene-coated graphite core electrode. In use the tip of the electrode is immersed into the sample fluid and connected to a potentiostat along with a suitable counter electrode and a calomel reference electrode. By keeping the potential of the working electrode at +100 mv to 300 mv relative to the calomel electrode, a current was produced which was proportional to the glucose concentration.
More recently an article by G. A. Robinson et al disclosed a redox electrode useful in electrochemically measuring immunoassays, see Clin. Chem., 31, No. 9, 1449-1452. However, the Robinson electrode had a magnetizable steel rod or bar magnet inside the electrode which contacted a pyrolytic graphite disc. In practice, Robinson constructed a sandwich-type, multiple-antibody immunoassay in which the analyte was bound to both a glucose oxidase conjugate and a separate magnetic solid phase conjugate. A pellet was formed by magnetically separating the sandwich components, when the electrode tip was placed in the solution, and washed twice with a buffer. After the addition of glucose and an electron transfer mediator (ferrocene), the electrode was placed in the solution along with a platinum auxiliary electrode and a calomel reference electrode, and the current was measured.